This study will attempt to analyze, define, and understand the mechanism of cellular control during the processes of regeneration, differentiation, and maturation of the hair and squamate epidermis. To provide a basis for experimental investigations further histological studies on the species variation of the squamate epidermis will be continued and enlarged. The shedding cycle of these animals will be evaluated in vitro and in vivo with respect to season and hormonal alteration. Ultrastructural studies of the distinctive strata and their species variation will continue. Experimental studies on the biophysical relationships of the various strata will be evaluated. Studies on the relationship between the shedding cycle and wound-healing in the squamates will be continued both at the histological, histochemical, and the ultrastructural level to further our understanding of the control mechanisms involved in cell movement, cell growth, differentiation and maturation. Organ culture of explants of squamate epidermis, and hair will be continued to evaluate specific factors, external, and intrinsic to the epidermis which control the cyclic alterations which occur within these organs. Variations in the structure of the cell membranes, cell organelles, and cytoplasm during maturation of the cells of the squamate epidermis will be studied by freeze-cleaving.